Nonito Donaire stopped Jorge Arce with left late in the third round Saturday night to retain the WBO super-bantamweight title and send the Mexican veteran into retirement.

Donaire, from the Philippines, improved to 31-1 with his 20th knockout. Arce dropped to 61-7-2.

"My left hook was a damaging hook tonight," Donaire said. "I felt very strong in the ring."

Donaire won in front of a raucous, mostly pro-Arce crowd of 7,250 at Toyota Center in Houston.

"The reason why people survive is because they are afraid to open up," Donaire said. "I have a lot of respect for [Arce] because he came in there and he opened up. He wasn't afraid. He was aiming to surprise me. But when he was opening up, that gave me the left hook and when I can throw sitting down on that left hook, everybody will go down."

The 30-year-old Donaire hasn't lost a fight in more than 11 years. He also knocked down Arce with about 2 minutes to go in the second round with a right-left combination.

"I'd promised my kids that If I lost this fight, I'd retire," said the 33-year-old Arce, a former world champion. "Fortunately, I have taken care of what I have earned through the years."

The fight headlined HBO's World Championship Boxing season finale, and the broadcast marked Larry Merchant's last after 35 years as a ringside boxing commentator for the network.

"All good things come to an end," Merchant told The Associated Press prior to the fight. "There will always be more fights. It was great to go out on a great fight like last week [Juan Manuel Marquez's knockout of Manny Pacquiao] and to be able to speak directly to all the fans of HBO Boxing for all these years."

Donaire said he wanted to fight the other top fighters in the division, Abner Mares and Guillermo Rigondeaux.

The 81-year-old Merchant was inducted into the International Boxing Hall of Fame in 2009.

"Thirty-five years on one show in television? I never imagined that it could go on for that long, because that is not what happens in the entertainment world."

An undercard fight between WBA super-bantamweight champion Rigondeaux of Cuba and Poonsawat Kratingdaenggym of Thailand was scratched after Poonsawat failed a physical this week.

Poonsawat was denied a license by the Texas Department of Licensing and Regulation after he failed blood tests. The reason for the failed blood tests wasn't disclosed.

Santa Cruz wins on network TV

Leo Santa Cruz defended his IBF bantamweight title with a unanimous decision over Alberto Guevara on Saturday in the first live boxing match on CBS in 15 years.

Santa Cruz (23-0-1, 13 KOs) won his third defence of his 118-pound belt in just over three months with steady aggression against Guevara (16-1), who performed well despite taking the fight on three weeks' notice.

Santa Cruz overcame an apparently injured nose by breathing through his mouth for most of the fight. He also fought through a right hand injury picked up in sparring, switching to a southpaw style while steadily breaking down Guevara with an impressive 989 punches in the 12-round bout.

"I've been fighting a lot lately, and I don't think I've been giving myself enough time to rest in between," said Santa Cruz, who just won his belt in June. "I'm sorry I didn't give that great of a show today. I felt a little different. ... Usually I throw more body shots, but I couldn't because he was running too much."

Judge Jonathan Davis scored it 116-112 for Santa Cruz, while Pat Russell had it 118-110 and Fritz Werner scored it 119-109. The Associated Press favoured Santa Cruz 117-111.

Although Santa Cruz apologized for his performance despite connecting with nearly twice as many power shots (210-112), the Los Angeles Sports Arena crowd didn't seem disappointed at all — but maybe that's because fans got in free for the first session of a long day of boxing created by CBS' decision to show Santa Cruz's fight on network television.

U.S. Olympian Joseph Diaz Jr. also won his pro debut in the afternoon session, knocking down Vicente Alfaro in the fourth round of a shutout decision. Two of Diaz's former U.S. teammates, Errol Spence and Marcus Browne, also won their second pro bouts by stoppage.

Former British 140-pound champion Amir Khan is slated to meet Carlos Molina in the main event of the evening session.

Santa Cruz wore a Santa hat on his ring walk, and his broad smile also indicated he wasn't overwhelmed by the scope of his network debut. Yet the Mexican-born champion who fights out of nearby Lincoln Heights promptly lost the first two rounds, with Guevara repeatedly beating him to the punch with combinations and superior movement.

Santa Cruz picked it up in the third, hurting Guevara with an early left hook before methodically going to work on Guevara with body shots and a superior work rate. Santa Cruz had the challenger in steady retreat for long stretches of the remaining rounds, and Guevara's relatively meagre power wasn't enough to back up the champion.

Santa Cruz controlled the second half of the fight, but failed to finish Guevara despite numerous big exchanges, including big shots early in the 12th round.

Diaz, from nearby El Monte, dominated his debut in front of a vocal hometown cheering section. Diaz, who narrowly lost his second bout at the London Olympics to world champion Lazaro Alvarez of Cuba, hopes to fight again next month.

"I was a little nervous, but I know I have to stay a little bit more relaxed," Diaz said. "I'll be better the next time. Fighting is fighting. I just didn't have headgear on this time."

In the final big fight of the night, Briton Amir Khan was a winner in a comeback bout against previous unbeaten but unproven Carlos Molina in Los Angeles.

Molina had some decent moments early but was non-competitive by the time his corner stopped the affair between the 10th and 11th. Khan improved to 27-3 with 19 knockouts.

Khan was knocked out in his last bout by Philadelphia fighter Danny Garcia, and lost a disputed decision to Lamont Peterson of Washington in the fight before that.

As a result of the consecutive losses, Khan switched trainers from Freddie Roach to Virgil Hunter, who works with unbeaten super middleweight Andre Ward.

With files from CBCSports.ca